试题题干
Directions: Read each of the following sentences carefully, and choose A,B,C or D that has the closest meaning to the underlined word or phrase.
This is an unexplored area in vitamin research and the only known advantages of vitamin E are confined to specialized medical cases.（）
参考答案
正确答案：
试题解析
restricted to 限于。这是维生素研究中未开发的领域，维生素E的唯一已知优势仅限于专门的医学病例。